Leadframe-based Ball Grid Array (LFBGA) has the advantages of higher packaging density, lower manufacturing cost, and better thermal dissipation. Leadless leadframes replace the traditional printed circuit boards or ceramic substrates with solder balls disposed on the leads of the leadframes. The solder balls are disposed in an array or in multiple rows to provide electrical connections to an external printed circuit board by SMT. Related technologies have been disclosed by R.O.C. Taiwan Patent No. 529770 and 584316.
A reflowing process is required for leadframe-based BGA to solder the solder balls on the leads of the leadframe. However, the reflow temperature to ensure good wetting of the solder balls may cause unrestrained bleeding of the fused solder to the undesired spots, leading to the insufficient heights of the solder balls or even bridging between the leads. A solution is provided by half-etching the leadframes so that only the soldering areas of the leads protrude from the other portions of the leads before die-attaching and molding processes, followed by an encapsulation process in a manner that the other portions of the leads are concealed by the encapsulant and the soldering areas of the leads are exposed from the bottom of the encapsulant. However, during encapsulation, the leadframes are laid on the molding chest or adhesive tapes with only the protruded soldering areas of the leads in contact with the supporting surfaces of the molding chest or tapes, and mold flashes therefore become an issue. Moreover, since the soldering areas of the leads and the bottom surface of the encapsulant are on the same plane so that mold flash can not easily be detected and removed leading to weakening soldering strength and dropping of solder balls.
Conventional manufacturing processes of leadframe-based BGA packages are disclosed in R.O.C. Taiwan Patent No. 567566. A non-conductive film with through holes to expose the soldering areas of the leads is attached to the bottom surface of the leadframe to serve as the solder mask. Since there are gaps between the leads, the non-conductive film must be pre-formed in compliance with the layout of the leads where extra costs are incurred due to the application of this additional material. Furthermore, when attaching the pre-formed non-conductive film on the leadframe, accurate alignment between through holes and the soldering areas is required. Once the through holes of the non-conductive film are not completely covered by the leads, encapsulant may flow into the through holes leading to failure of solder ball joint.